The present invention relates to an aqueous resin composition, which can be used mainly as a paint, primer, ink, adhesive and sealant. Moreover, the inventive resin composition is possible to be used by formulating to other aqueous resins and water-soluble resins such as aqueous urethane, acrylic, polyester and epoxy depending on the uses, hence it can also be utilized as a modifier of film forming materials.
Above all, since it allows to form a film and adhesive layer excellent in the adhesiveness, flexibility and water resistance particularly onto polyolefin substrate at, having a nonpolar surface, it is useful as a resin for the parts of car etc., paints for polyolefin film, polyolefinic mold, etc., primer, ink, sealant and adhesive.
Conventionally, modified polyolefin compositions modified polyolefins such as polypropylene, polyethylene and copolymer of propylene, ethylene and .alpha.-olefin with unsaturated carboxylic acid or acid anhydride and acid-modified chlorinated polyolefins chlorinated them further are used for painting material, primer, ink, etc. In the present circumstances, however, these resins dissolve only into aromatic organic solvents such as toluene and xylene, hence a large quantity of organic solvent cannot help being used, posing the problems from the safety and health and environmental pollution.
For this reason, in recent years, an aqueous resin with aqueous conversion performed by adding polyol, surfactant and basic substance to chlorinated polyolefin (U.S. Pat. No. 340,845 ), an aqueous resin aqueous-converted chlorinated polyolefin acid-modified with unsaturated carboxylic acid or acid anhydride by using surfactant and basic substance (Japanese Patent Application No. Hei 01-323506), and the like are applied.
In addition, attempts to produce aqueous dispersions of chlorinated polyolefin have been made, which are disclosed in, for example. Japanese Unexamined Patent Publication No. Hei 1-153778, No. Hei 1-256556, No. Hei 2-284973 and the like, but these use the aromatic organic solvent on production, thus complete elimination thereof was difficult. Moreover, attempts to produce aqueous dispersions of modified polyolefin have also been made, which are disclosed in, for example, Japanese Unexamined Patent Publication No. Sho 59-47244, No.-Hei 2-286724 and the like. However, in the painting, adhesion, etc., they have drawbacks of adhesiveness and water resistance, poor paintability, etc., when the coating articles and adhering articles are polyolefin resins, hence such aqueous compositions have not still come to the practical use. Moreover, in Japanese Unexamined Patent Publication No. Hei 3-182534, the improvement in the performance of coated film is intended by performing the aqueous conversion of modified chlorinated polyolefin using surfactant and further by formulating aqueous polyurethane resin.
However, because of the nonreactivity of water-soluble urethane resin and surfactant, the active ingredient dissolves out from coated film by water causing a phenomenon of decreased water resistance due to the defect of coated film that seems to take place through it.
Moreover, when forming the film using aqueous converted chlorinated polyolefin resin with aqueous conversion performed by using polyol and surfactant, the hydrophilic ingredients such as polyol and surfactant are left behind in the film and they dissolve out by moisture resulting in a drawback of low water resistance of film.
Furthermore, since the chlorinated resin ingredient is contained in large quantities, not a few problems arose in the abolition and recycling treatment of final product with film, adhesive layer, etc. formed.
Whereas, the inventors made an application on an aqueous resin aqueous converted polyolefin resin, chlorinated polyolefin-resin or acid-modified polyolefin resin by using a reactive surfactant (Japanese Patent Application No. Hei 04-256935. No. Hei 04-256936 and No. Hei 04-256937). These inventions aim at the improvement in the water resistance of film by fixing the hydrophilic substances present in the film to film.
The reactive surfactant has been used on emulsion polymerization up to now. It has a surface activity to suspend monomer into water during the emulsion polymerization and, because it reacts with other monomer, it is taken in the structure of polymer bringing an effect on the improvement in the water resistance of reaction product as a result.
However, when comparing with nonreactive surfactant having similar structure thereto, the reactive surfactant has lower dispersibility of resin, hence the addition level had to be made higher or other polyol, nonreactive surfactant, etc. had to be used in combination for obtaining a stable aqueous conversion product.
Aqueous block isocyanates are used generally for fiber processing, crosslinking agent and modifier of resins such as latex, acrylic and urethane, surface processing of plastic film, And the like, but there are no reports that have found novel uses and features by combining them with aqueous polyolefinic resin.
Moreover, when introducing the crosslinking structure by combining with block isocyanate and further fixing the hydrophilic ingredient, too, the use level of block isocyanate was limited to maintain the adhesiveness of formed film to substrate and, in particular, it was needed to decrease the hydrophilic substance having active hydrogen reacting with isocyanate as little as possible to improve the water resistance of film and maintain the adhesiveness to substrate.
On the other hand, the aqueous conversion of polyolefinic resin is generally performed by a method that, after the resin raw material was dissolved into some solvent, hydrophilic ingredients such as surfactant and basic substance are added and then the solvent is substituted by water.
Moreover, a method that the raw material resin, surfactant and basic substance are mixed and molten at a temperature above the melting point of resin and then water is added gradually thereto to cause the phase inversion, thus performing the aqueous conversion. This method however is performed traditionally under ambient pressure, hence, in the case of raw material resin having high viscosity below 100.degree. C. and the like, the addition of water decreased the temperature of resin to increase the viscosity of molten liquor, resulting in decreased stirring efficiency and in capability of homogeneous phase inversion in many cases.
As described above, conventional modified polyolefin compositions were used as solutions in organic solvents, hence the toxicity of solvent, environmental problems, etc. raised a question. Moreover, around the aqueous resin compositions using surfactant, which were contrived in an attempt to solve them, the controversial point of water resistance hung hitherto. The purpose of the invention is to provide an aqueous resin composition simultaneously solvable all of these toxicity, environmental problems and poor water-resistant performance of coated film.
Moreover, the invention aims at the solution of a problem of residual solvent involved in the conventional method of aqueous conversion of polyolefinic resin and a problem of residual undispersed solids causing through the heterogeneous phase inversion as well.
Furthermore, the invention aims at the improvement in the water resistance without injuring the adhesiveness and adhesion of film formed with the aqueous resin composition of polyolefin or modified polyolefin to substrate in the use of said aqueous resin composition.
As a result of diligent investigations on the aqueous resin composition, which has no problems such as toxicity and pollution, thus being excellent in the safety and which is excellent in the water resistance without injuring the adhesiveness and adhesion, to attain said purposes, the inventors have reached the invention.
By using the block isocyanate the isocyanate group of which are blocked and do not react with water, it does not react with water in the steps of aqueous conversion adding water to modified resin and of coating of aqueous resin composition onto substrate and drying, but it is deblocked to have activated isocyanate group when it is subject to the heat treatment further at higher temperature after drying or when it is subject to the heat treatment by baking at a temperature higher than the drying temperature after other film-forming component was overcoated. The activated isocyanate group reacts with surfactant remaining in the film ingredient, modified polyolefin or other hydrophilic groups such as hydroxyl group, carboxyl group and amino group present in the overcoating paint etc. In this way, when using in combination with modified polyolefin resin, an improving effect on the water resistance of film has been found by fixing the hydrophilic ingredient or transforming the hydrophilic functional group into more hydrophobic functional group without injuring the characteristics of polyolefin.
In addition, upon preparation of the aqueous resin composition, it has been found that, by using poly(alkylene oxide) derivatives with a solubility parameter (SP value) of not lower than 7 to not higher than 12, stable aqueous conversion product can be obtained effectively in less amount over the cases using alcohols, low-molecular weight glycols or other surface-active ingredients. Moreover, when using the surface-active ingredients described in the invention in combination, it has been found that the affinity of aqueous solvent to resin improves, thus the use level of surfactant can be decreased further. Such effects appeared also in the cases of combined use of hydrophilic third ingredients such as other surfactants, alcohols and glycols.
In consequence thereof, the amounts of hydrophilic ingredients and hydrophilic functional groups in the film formed with the aqueous resin prepared could be decreased, thereby remarkably improving the water resistance of film. This effect appeared also in the case of combined use of block isocyanate and it has been found that the water resistance of film can improve even more over the case of using conventional aqueous converted polyolefin resin with aqueous conversion performed by using alcohols, low-molecular weight glycols and surfactants in combination with block isocyanate.